This invention relates generally to packet storage/exchange nodes and more particularly to a multi-destination communication processing system in a packet storage/exchange node. The invention is suitable for excluding an abrupt increase in load on multi-destination message expansion processing and avoids mutual interference at message input and output of a subscriber circuit due to a bottleneck in node performance.
The term "terminal" is a general term indicative of packet exchange terminals such as computers, facsimile terminals and the like. The term "node" is a general term indicative of network elements having a packet exchange function.
A prior art packet storage/exchange node is generally constructed as shown in FIG. 1. Referring to FIG. 1, a line control module 1 controls transmission and reception of a message in the form of a packet to and from a telephone line such as a telephone subscriber line or telephone trunk line 10. A file control module 2 stores a message from the line control module 1 into a predetermined area of a file storage 3 and reads a message from the file storage 3 to supply the read message to the line control module 1. The file storage 3 stores messages in correspondence to individual single destination deliveries.
In designing such a packet storage/exchange node with a view of meeting an increase in load on the file control module, it has hitherto been practice to increase the number of file control modules involved correspondingly to thereby promote the capability of the node in total. This expedient is exemplified in FIG. 2 wherein a plurality of file control modules 2-1, 2-2 and 2-3 are provided.
With multi-destination message services introduced into the packet storage/exchange node, however, the load on the file control module is theoretically increased in proportion to (n-1) when the number of subscriber terminals associated with the node is n and the prior art system faces difficulties in complying with the increasing load. Consequently, there arises a problem that a multi-destination message from one of the subscribers interferes with communications in progress between the node and an other subscriber, causing a bottleneck in the file control module processing.
This will be detailed with reference to FIGS. 3A-3C. As illustrated in FIG. 3A the preformance of the file control module 2 is set to be such that the load factor typically measures 100% when n subscribers access the node at a time. Under multi-destination message services, multi-destination message expansion is required to be undertaken at the entrance to the file control module 2. As will be seen from FIG. 3B one multi-destination message for the total (n) deliveries issued from one subscriber occupies (n-1)/1.times.100% of the load factor of the file control module. Likewise, as illustrated in FIG. 3C, multi-destination messages for the total deliveries issued from n subscribers will load n.times.(n-1)/n.times.100=(n-1).times.100% of the file control module's load factor upon the file control module 2. As a result, the node experiences, in its file control module, such a bottleneck as is liable to force the file control module to continue occupying the CPU at an activity ratio of about 100%, followed by stoppage of processings of lower priority grade or to fill up the input/output buffer to make the same inoperable. This means that the node becomes overloaded instantaneously.
Reference may be made to JP-A-58-204660, for example, as a relevant reference to multi-destination communications.